Make no mistake, the Niners' decision to trade Buckner to the Indianapolis Colts for the No. 13 selection in this year's NFL draft was painstaking and the team is worse for it. San Francisco wanted to keep Buckner around for the long haul but concluded that the cost was going to make it difficult to retain other key players.
So, the 49ers swallowed that bitter pill and used the resources to re-sign the likes of defensive linemen Arik Armstead and Ronald Blair III, free safety Jimmie Ward and offensive lineman Ben Garland and extend second-round tenders to receiver Kendrick Bourne and running back Matt Breida.
Still, Buckner's absence creates a massive hole in the middle of the 49ers' defensive line, which was its greatest strength a year ago. Buckner was not only productive -- 28.5 regular-season career sacks and consistently drawing the most double-teams on the line -- but incredibly durable, missing one game and playing 3,347 snaps, third most in the league among defensive linemen, in his four seasons.
Which begs this question: How do the 49ers go about replacing a player who has been invaluable?
The Niners' ideal solution for replacing Buckner could be summed up in two words: Solomon Thomas. Thomas was the No. 3 overall pick in the 2017 draft. At the time, many league observers believed his best position in the NFL would be 3-technique defensive tackle.
That spot was already spoken for by Buckner, who rarely came off the field. That left Thomas attempting to find a home on the outside and, occasionally, kicking inside in pass-rushing situations. The results have been disappointing, as Thomas has struggled to find his way. He has 93 tackles and six sacks in three seasons, leaving the Niners unlikely to exercise the fifth-year option on his rookie contract this summer.
With Buckner gone, Thomas should finally get an opportunity to play more snaps at his ideal position. In fact, Buckner unknowingly offered a primary reason why Thomas could eventually fill his role when he called Thomas the second-most "explosive" player off the ball on the team behind only end Dee Ford.
“Solomon is a very explosive player," Buckner said in January. "Third down, he can rush the passer, and also in the run game, especially going against guards, getting on them quick, and he's a strong dude. So, when he has leverage, he's scary to see inside.”
The question with Thomas is whether he has enough bulk to hold up against the run, which could mean the Niners toy with multiple combinations inside. As it stands, Nick Bosa and Armstead are locked into a starting end spots, with D.J. Jones at nose tackle.
In addition to Thomas, the 49ers also brought back Blair, who is versatile enough to play inside and out, and have promising young tackle Kevin Givens. Kentavius Street and Jullian Taylor are also slated to return from injuries, though Street has yet to prove he can stay healthy and produce and Taylor projects more as a nose tackle. Sheldon Day also could return, though he remains a free agent.
Most likely, if the Niners don't make a significant outside addition at defensive tackle, Thomas will get the first opportunity, with the possibility that Armstead could kick inside with Jones when Ford is on the field in obvious passing situations.
For the most part, the big-ticket names on the free-agent market already have signed. Of the remaining defensive tackles on the market, Ndamukong Suh is the best available but likely would command more than the Niners are willing to pay. He isn't necessarily a fit, even though he has previously played for defensive line coach Kris Kocurek.
Aside from Suh, the pickings are slim -- Denver's Shelby Harris could be an intriguing option if his price tag is reasonable -- but the Niners could continue to monitor the market and see if anything appealing pops up as teams potentially let go of tackles who could fit.
Given San Francisco's limited cap space and need to extend more of their own key players such as tight end George Kittle, this seems like an unlikely route to help replace Buckner, barring a bargain that pops up late.
The 49ers have never been shy about taking defensive linemen in the first round of the draft. They have done it in four of the past five drafts. The front four is the strength of the team and the Niners are willing to do what's necessary to ensure it stays that way.
Armed with pick Nos. 13 and 31 in this year's draft, it wouldn't be a surprise if San Francisco used one of those choices on someone to help fill Buckner's void.
If the 49ers choose to go that route with the 13th pick, there are two defensive tackles above the rest in Auburn's Derrick Brown and South Carolina's Javon Kinlaw. While both are considered good enough to go before the Niners are on the clock at No. 13, either would be enticing if they slipped to San Francisco's spot.
Brown is a big (6-foot-5, 326 pounds) and powerful pocket pusher who plays with the type of violence Kocurek covets. Kinlaw is a bit more of a raw prospect but is almost as big (6-5, 324) and powerful. ESPN's Todd McShay ranks Brown No. 5 and Kinlaw No. 6 in his overall rankings.
TCU's Ross Blacklock is another top prospect who is a bit smaller (6-3, 290) but a better athlete capable of pushing the pocket as a pass-rusher and could end up in the top 20. McShay ranks Blacklock No. 12 on his big board.
Aside from that top three, others to watch should the Niners wait until No. 31 (or trade down) include Texas A&M's Justin Madubuike, Oklahoma's Neville Gallimore, Baylor's James Lynch and Missouri's Jordan Elliott.
It's a safe bet the Niners will add to the defensive line at some point in the draft. Whether it happens again in the first round likely depends on who is available when they pick and how they stack up against the top receivers, offensive linemen and cornerbacks still on the board.